Lecture 4A Demand for Water

Demand for Water
CIVWARE

Dr. Danilo C. Terante
Head, Hydraulics and Water Resources Engineering
Civil Engineering Department
De La Salle University
Chairman, Water Engineering Specialty Division
Philippine Institute of Civil Engineers - National

Development of Water Resources
How much water is needed? How much water is available? How are the requirements satisfied by the supplies?
How is the used-up water disposed? Demand for Water Supply
Withdrawal uses

Nonwithdrawal uses

Consumptive uses

Involve diversion of surface water or groundwater from its sources

Involve on-site uses

Involve portion of withdrawn quantity which is used by crop

Municipal requirements
Water requirement category

Large industrial requirements
Waste dilution requirements

Municipal Requirements

Required quantity = (population at the end of design period) x (per capita usage)

Population forecasting

Population Forecasting
Short-term Estimates
Graphical
Extension Method
Arithmetic Growth
Method

Geometric Growth
Method
Declining Growth
Rate Method

Graphical Extension Method

Consists of plotting the population of past census years against time and fitting the best curve Curve is extended into the future to obtain the projected population.

Arithmetic Growth Method

Pt  Po  K at
Pt = projected population t years after Po
Po = present population t = period of projection
Ka = uniform-growth rate constant

P2  P1
Ka 
t
P1 and P2 are recorded population at some Δt interval apart.

Example
The population of District 5 of the City of Manila has been recorded in 1980 and
1995 as 400,000 and 440,000, respectively. Estimate the 2011 population assuming arithmetic growth.
440,000  400,000
15
8000
Ka 
3
Ka 

 8000 
P2011  440,000  
16
 3 
P2011  482,667 persons

Geometric Growth Method

ln Pt  ln Po  K Pt
Pt = projected population t years after Po
Po = present population t = period of projection
Kp = uniform-growth rate constant

ln P2  ln P1
Kp 
t
P1 and P2 are